Photocatalytic Isomerization of Stilbenes via Molecular Recognition With a Dual‐Function η 6 –Arene Catalyst

ABSTRACT Electron donor–acceptor (EDA) complexes, formed through noncovalent interactions between electron‐rich and electron‐deficient species, can undergo photoinduced charge transfer to access reactive radical intermediates. However, rapid and unproductive back electron transfer (BET) limits their synthetic utility. Herein, we report a dual‐function ( η 6 –arene)rhodium(III) catalyst that enables contra ‐thermodynamic E ‐to‐ Z isomerization of stilbenes via selective EDA complexation. In contrast to well‐studied photoisomerization reactions driven by triplet photosensitizers via intermolecular energy transfer (EnT), photoexcitation of the self‐assembled EDA complex generates a charge‐separated singlet exciplex that undergoes back electron transfer coupled with intersystem crossing to populate a localized triplet‐state olefin intermediate. The catalyst plays two pivotal roles: the metal‐bound arene scaffold enables molecular recognition of planar ( E )‐stilbenes over twisted ( Z )‐isomers through noncovalent interactions, while the heavy rhodium atom promotes ISC.